Any of a number of programing errors, client malfunctions, imbalanced gameplay, random server downtimes, extended maintenance, or other failures on the part of Riot Games in regards to it's free-to-play game League of Legends.

Player One (12:23): why does it still say he is online?
it did this when you quit also
Player Two (12:23): idk ?.?
Riotfails?